The present invention relates to a gasket type pressure sensor mounted on a vibrating body such as a cylinder head of an engine generating vibration derived from knocking and fuel injection, and used to detect pressure fluctuation by means of piezoelectric elements.
A pressure sensor of this type is, for instance, inserted between the gasket seat face of an engine spark plug and the plug seat of a cylinder head to secure the pressure sensor to the surface of a vibrating body by utilizing the contraction of a proper screw body. The vibration generated by the vibrating body causes the piezoelectric element to produce compressive distortion and an output signal synchronous with the vibration is obtained from the piezoelectric element. The pressure sensor is used to detect pressure fluctuations at the time of knocking and fuel injection when, as aformentioned, it is applied for use in the cylinder head.
As shown in FIG. 6, there has been developed a pressure sensor having an integrated body covered with a metal case, the integrated body comprising piezoelectric elements and a presser metal.
The manufacture of such a conventional apparatus comprises piling two piezoelectric elements a, a with an electrode b sandwiched therebetween; further mounting an inverted T-shaped presser metal c in cross section with an upwardly projected pressure-receiving portion d on the above combination, the pressure metal c being made of material having a low coefficient of expansion such as Invar and Kovar brand iron alloys, trademarks of Westinghouse Corp.; and 42Ni-Fe with a pressure receiver d; covering the combination thus built with a metal case e; caulking the ends of the metal case e inward by the shoulders of the pressure receiver d; and upwardly projecting the pressure receiver d.